The present invention relates to a screw connection element and to a protective covering applicable on an outer thread portion thereof.
Pipes, components having pipe-like connections, valves, fittings or the like and also connection and extension parts therefor are connected to each other in every respect by screw connections in particular in the sanitary and heating field but also in machine construction. For this purpose, one of the parts to be connected has an outer threaded portion and the other part a corresponding inner threaded portion. Since as a rule fluid in the form of a liquid or a gas (e.g. water or air) flows through both parts, the screw connections must fulfil not only mechanical strength requirements but must also be fluid-tight at normal pressures (e.g. up to 10 bar).
Whilst fulfilling the strength requirements does not represent a problem, the production of a long-lasting durable seal still poses difficulties. It is in fact generally normal to cover the outer threaded portions before joining with hemp fibres, plastic material (Teflon) strips or other sealing means, yet this measure, irrespective of whether the cooperating threaded portions are made of metal or plastic material, has proved to be inadequate. A main reason for this resides in the fact that the quality of the seal usually depends upon the care with which the personnel applying the sealing means and then producing the screw connection operate. In the commercial field, it can be assumed that in fact good seals are obtained in most cases, but the number of unserviceable seals continues to be far too great. In addition, it is frequently not taken into account that screw connections must be unscrewed again often by up to 90° after tightening in order for example to straighten up a fitting which is sitting at an angle and therefore disposed in an optically unpleasant manner. Unscrewing of this type results not infrequently in a lack of seal in the initially tight screw connection.
It is known in order to avoid problems of this type to provide one of the threaded portions with an integrated sealing means in the factory, in that for example the threads are produced at least partially from an elastic material, such as e.g. PEX or EPDM (EP 1 004 804 A1) or a threaded portion is provided with an annular groove and a sealing element inserted therein (EP 0 544 111 B1, EP 0 751 328 A1). In addition, separate sealing elements are known which have respectively one stop ring which can be screwed onto an outer threaded portion and a sealing mass which is fixed on the latter, can be screwed onto the outer threaded portion and is made of rubber, plastic material (Teflon) or the like, which is squeezed during production of the screw connection between the stop ring and the inner threaded portion (EP 0 523 775 A1). However all these measures have to date not proved to be satisfactory.